Process for the protective treatment of iron



- Patented June 30, 1953 UNITED STATES NT OFFICE PROCESS FOR THEPROTECTIVE TREATMENT OF IRON York No Drawing. Application May 29, 1950,Serial No. 165,109

Claims. 1

This invention relates to a process for the protective treatment of ironand has particular relation to a process of this type in which metallicaluminum is applied to and alloys with the iron surface to be protected.

The main object of the present invention is to provide an improvedprocess for the protective treatment of iron by the application ofaluminum chloride in the vapor phase to the surface to be protected inorder to obtain a more efiicient and durable protection of the iron,than obtainable by the hitherto known processes using aluminum.

Another object of my invention is to provide an anhydrous gaseousmixture, in which vaporized aluminum chloride is present in intimatemixture with hydrogen and which is particularly adapted to react quicklywith the iron and to produce an improved corrosion-resistant surfacelayer.

A further object of my invention consists in providing a process for theprotective treatment of iron with a mixture of aluminum and copper.

It is also an object of my invention to produce from silicontetrachloride and suitable organic compounds completely dry gaseous HClwhich can be used with advantage in the production of a metalchloride-hydrogen mixture needed in carrying out my invention.

Other objects and the advantages of the invention will be apparent fromthe appended claims and the following specification, which illustrate byway of example some embodiments of my invention.

It has been previously suggested to apply certain compounds of aluminum,particularly A115, to the surface of iron in order to obtain a corrosionresistant surface coating comprising aluminum and iron. However, it wasnot hitherto possible to isolate a compound of the formula All and it isdoubtful whether such a compound can be prepared at all.

It has also been suggested to place iron articles to be treated in adrum or the like with a mixture of powdered aluminum, aluminum oxide andammonium chloride, to rotate the drum and heat it in a hydrogenatmosphere in order to provide the articles with a corrosion resistantsurface. It has been found that this process does not give satisfactoryresults.

I have now found that the application of metallic aluminum to iron canbe carried out in a satisfactory manner and yields products having asurface of high resistance to corrosion particularly at elevatedtemperatures by proceeding in the manner described hereinafter.

According to my present invention, the iron surface to be protected istreated with a gaseous mixture which contains vaporized AlCls andhydrogen and has been obtained by reactingmetallic aluminum withcompletely dry H01 gas in the manner described further below. Incarrying out this procedure, the AlCls is used in dry condition and isapplied to the iron in the absence of water or moisture in an atmosphereof hydrogen. Both conditions must be observed, as the absence of water,steam or moisture as well as the presence of a hydrogen atmosphere areessential.

In carrying out the process of my invention, dry gaseous HCl gas iscaused to pass at a temperature between 300 and 600 C. over a mixture ofaluminum, which may be present for example in the form of shavings orgrit, with aluminum oxide (A1203) and small coal. The aluminum oxide maybe used in an amount of 10% by weight and the coal likewise in an amountof 10% by weight based on the amount of aluminum. The aluminum issubjected to the action of HCl as in mixture with aluminum oxide andcoal in order to prevent sticking together of the metal particles.Moreover, the coal prevents oxidation and combines with water vapor ifthe latter is present. No water is formed by a reaction between A1203and HCl in the above mentioned temperature range of 300 to 600 C., assuch reaction does not set in below 800 C. The HCl gas reacts with themetallic aluminum according to the equation and this reaction providesfor the presence of the necessary hydrogen in my process. As thealuminum is present in great excess in the reaction, it is possible thatsub-chlorides of the formula AlCl and/or AlClz are also formed to someextent I have found that the anhydrous gaseous mixture obtained in theabove described manner and consisting of an anhydrous intimate mixtureof vaporized aluminum chloride and hydrogen, can be used with excellentresults in the production of a protective layer on iron. In order toobtain such layer, said gaseous mixture is passed over iron heated to atleast 700 C. and preferably 900-l000 C. or higher, up to 1200 C. Uponbringing the gaseous mixture in contact with the heated iron, thealuminum chloride is split into Al and C1, the aluminum forming an alloywith the surface layer of the iron, while the Cl is converted into ironchloride. The thickness of the alloy layer formed depends upon thetemperature and duration of the treatment of the iron with the gaseousstream of aluminum chloride and hydrogen.

I have also found that the protective efiect of my process can beincreased by using the aluminum in combination with copper. This can bedone for example by using a mixture of aluminum shavings and coppershavings or by using an alloy of aluminum and copper in the reactionwith dry gaseous HCl. In this case a gaseous mixture containinghydrogen, aluminum chloride and copper chloride is formed and in thetreatment of the heated iron with such mixture in the above describedmanner, in addition to aluminum, copper is also deposited in the ironand increases the resistance of the iron to corrosion. I use for examplea gaseous mixture containing 2% by weight of copper based on the weightof Al in the gaseous mixture, and found that admixtures of copper to Alvarying between 1 and 5% give good results.

The duration and temperature of the treatment according to my inventiondepends on the requirements of resistance of the iron to corro sion. Ihave found that treatments with the gaseous AlCh-containing mixture at900 to 1000 C. during to 60 minutes give satisfactory results. In orderto decrease the brittleness of protective layers in iron treatedaccording to the process of my invention, the latter may be subjected toa thermal after-treatment at about 1000 C. in an atmosphere of hydrogenor air. Such treatment causes the aluminum to diiluse deeper into theiron so that concentration of aluminum in the top layer of irondecreases and said layer becomes softer.

I have found that a, completely dry stream of I-ICl gas can be obtainedwith advantage by reacting silicon tetrachloride with an alkanol, forexample ethyl alcohol, methyl alcohol, propyl alcohol, butyl alcohol,whereby a completely dry stream of H01 gas and a compound for example ofthe formula Si(OC2H5) 4 is obtained which can be used in a manner knownby itself for the preparation of silicone resins. It will be understood,however, that HCl gas prepared in any other suitable manner may also beused in carrying out my invention, provided that it is in asubstantially anhydrous condition.

It is essential in carrying out my invention that the iron is treatedwith a gaseous mixture obtained by the reaction of metallic aluminum anddry HCl gas.

It will be understood by those skilled in the art that my invention isnot limited to the specific steps, conditions and materials describedabove and may be carried out with various modifications. For example,instead of reacting the aluminum with H01 in the form of shavings orgrit, it can be used in the form of powder or other suitable form. andin combination with admixtures other than aluminum oxide and/or coal.The temperature and duration of the treatment of iron with the mixtureof vaporized AlCls and hydrogen may be varied and the amount of copperused in combination with aluminum may be varied within the limits statedabove. These and other modifications may be made without departing fromthe scope of the inventionas defined in the appended claims.

What is claimed is:

1. A process for the protective treatment of iron, comprising causingiron to react at 700 to 1000 C. with an anhydrous gaseous mediumconsisting of hydrogen and aluminum chloride and obtained by thereaction, at 300 to 600 C'., of anhydrous HCl gas and a mixture ofaluminum, aluminum oxide, and coal, until a coating of aluminum isdeposited on the surface of the iron treated. I

2. A process for the protective treatment of iron, comprising causingthe iron to react at 700 to 1000 C. with an anhydrous gaseous mediumconsisting of hydrogen and aluminum chloride and obtained by thereaction, at 300 to 600 C., of anhydrous H01 gas and a mixture ofmetallic aluminum and copper, aluminum oxide, and coal until a coatingis deposited on the surface of the iron treated.

3. A process for the protective treatment of iron, comprising causingiron to react at 700 to 1000 C. with an anhydrous gaseous mediumconsisting of the reaction product, formed at 300 to 600 C, of anhydrousI-ICl gas and aluminum and copper, in mixture with aluminum oxide andcoal, until a coating is deposited on the surface of the iron treated.

4. A process for the protective treatment of iron, in which the productobtained according to claim 1, is subsequently subjected to heating atabout 1000 C.

5. A process for the protective treatment of iron, as claimed in claim1, in which anhydrous 1161 gas obtained by reacting SiCh with analcohol, is used.

JOHANNE S FISCHER.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Mellors Modern Inorganic Chemistry, pages 398 and 399.

1. A PROCESS FOR THE PROTECTIVE TREATMENT OF IRON, COMPRISING CAUSINGIRON TO REACT AT 700* TO 1000* C. WITH AN ANHYDROUS GASEOUS MEDIUMCONSISTING OF HYDROGEN AND ALUMINUM CHLORIDE AND OBTAINED BY THEREACTION, AT 300* TO 600* C., OF ANHYDROUS HCI GAS AND A MIXTURE OFALUMINUM, ALUMINUM OXIDE, AND COAL, UNTIL A COATING OF ALUMINUM ISDEPOSITED ON THE SURFACE OF THE IRON TREATED.